This invention relates to a multicylinder vapor powered reciprocating engine and, more particularly, to such an engine having the inherent capability for restarting after a total stop solely in response to the availability of working fluid vapor at a predetermined condition regardless of crankshaft position when the engine last ceased operation.
There are many circumstances where rotary mechanical power from a totally self-contained unit is highly desirable, e.g., to power an artesian pump in a remote desert location where the only source of energy is the sun. The engine should operate over a long period of time without the need for any external source of electricity or manual inputs to restart it after a stop or to control its operation between stops. It is also absolutely essential that the engine, when provided with working fluid vapor at a predetermined condition, has the capacity for starting automatically, operating satisfactorily thereafter, ceasing operation when working fluid vapor is no longer available at the predetermined condition, and stopping in readiness for the next automatic restartxe2x80x94all without human intervention except for repair or scheduled maintenance.
Conventional closed loop solar collector systems typically are designed to include one or more electrically-operated servo-type valves to control engine vapor intake and to regulate the output of the engine to maximize operational efficiency. Such controls, however, require an external source of electrical power and are not particularly suitable for unattended operation over prolonged periods of time in remote areas. Likewise, it is preferable to eliminate the need for manual controls. Furthermore, it is highly desirable to completely seal-in the operating components of the engine to preclude contamination by dirt, moisture and other ambient pollutants and to maintain within the engine a subatmospheric pressure or vacuum for higher operational efficiency.
In my earlier issued U.S. Pat. No. 4,698,973, titled xe2x80x9cCLOSED LOOP SOLAR COLLECTOR SYSTEM POWERING A SELF-STARTING UNIFLOW ENGINExe2x80x9d, issued on Oct. 13, 1987 and incorporated herein by reference, there is disclosed and claimed a closed loop solar collector system that receives collected solar energy to vaporize a working fluid for delivery to a single piston uniflow system. The disclosed engine includes a single piston capable of acting directly upon a pair of normally closed intake valves projecting into the engine cylinder to actuate the same. Under relatively low pressure conditions in the boiler or vaporizing unit, a spring-loaded connecting rod facilitates control of the engine so that, in principle, the engine has the ability to start when available working fluid vapor attains a predetermined pressure and, thereafter, changing over from a start-up mode to a normal running mode of operation when the rotational speed of the engine attains a predetermined mode-change value. It is believed, however, that a single piston reciprocating in a single long cylinder could possibly come to a stop in an end-of-stroke position that may frustrate a subsequent restart. In other words, to promote wide use of uniflow engines with closed loop solar powered systems, it is believed necessary to have a sealed-in engine that will always start when working fluid vapor is delivered at a certain minimum pressure regardless of the engine crankshaft position when it comes to a stop.
The present invention, therefore, provides a multicylinder uniflow engine designed to restart readily no matter what position the crankshaft takes when the engine comes to a stop. The engine will always restart when working fluid vapor is available to the engine at a predetermined condition, e.g., when the static pressure of the working fluid vapor exceeds a predetermined value.
It should be appreciated that an engine of the type taught in this invention preferably should have as few mechanical moving parts as practical, be capable of completely sealed-in operation, and have a simple sturdy design, e.g., not be dependent on springs that may lose their elasticity or break over time, so that it will not require expensive or difficult production techniques or maintenance after installation.
It is, accordingly, an object of this invention to provide a multicylinder engine utilizing pressurized working fluid vapor (xe2x80x9cincoming vaporxe2x80x9d hereinafter) which will start automatically when one or more selected engine operating parameters meet corresponding predetermined criteria.
Another object of this invention is to provide a multicylinder, self-starting, simple engine suitable for integration into a closed loop solar energy collection system that generates a supply of working fluid vapor.
Yet another object of this invention is to provide a multicylinder uniflow engine of which most operating components are sealed-in to operationally communicate solely with a closed loop vapor system for providing to and receiving therefrom incoming vapor at a predetermined working condition.
Related further objects of this invention are to provide a multicylinder uniflow engine with a common crankshaft that will start in any position of the crankshaft when incoming vapor is made available at not less than a predetermined working pressure with or without rotating control elements.
Another related object of this invention is to provide a multicylinder uniflow engine with a common crankshaft that will start in any position of the crankshaft when incoming vapor is made available at not less than a predetermined temperature.
An even further object of this invention is to provide a multicylinder uniflow engine which upon starting from a total stop initially operates in a xe2x80x9cstart-up modexe2x80x9d characterized by the utilization of incoming vapor at a relatively high inlet pressure without expansion during a corresponding piston stroke in each cylinder, followed upon the attainment of a predetermined engine operating condition by a normal running mode characterized in that incoming vapor at high inlet pressure is received for only an initial portion of each working stroke and thereafter expands for the rest of the working stroke for efficient engine operation.
These and other objects of the invention are realized by providing in a self-starting, multicylinder, single crankshaft, reciprocating piston engine supplied with an expandable working fluid and having at least three cylinders evenly distributed around a common crankshaft, a first means for forcibly adjusting position in response to an output speed of the engine and a second means for controlling the start and stop of inflow of the working fluid sequentially into the cylinders as a function of the individual piston positions with respect to TDC during their working strokes in correspondence with the instantaneous position of the first means.
In different aspects of the invention, control of the engine operation from zero speed, through a xe2x80x9cstart-up modexe2x80x9d (during which working fluid moves the pistons without expansion), through a predetermined mode change speed and into a xe2x80x9crunning modexe2x80x9d (during which a charge of working fluid expands during each piston working stroke), is effected in response to an engine output rotational speed, or the pressure or temperature at which the working fluid is available.
In one alternative embodiment of the invention, a relief valve is provided in the head of each piston and is actuated during operation of the engine by inertia forces only, thus avoiding the use of springs and problems incidental thereto.
In a further improvement of the invention a mode change/fine-tuning valve mechanism is provided to ensure optimum utilization of the enthalpy provided to the engine in the working fluid.
Another improvement of the present invention contemplates vertically extending cylinders distributed in-line along a horizontally extending common crankshaft connected to the pistons reciprocating in the cylinders. Such a configuration permits working fluid condensate to drain from the engine cylinders under gravity when the engine shuts down.
An even further improvement of the invention contemplates a mode switch valve mechanism including a check valve and a control piston that cooperate to maximize engine efficiency by limiting the initial volume of working fluid permitted into the engine cylinders so that the working fluid can expand to an optimum six times the initial volume during each piston working stroke.
Another improvement of the present invention contemplates a piston having a head or crown portion including only surfaces that are fixed relative to the piston to conserve working fluid in the engine and simplify the piston structure.
Another improvement of the present invention contemplates an inlet valve assembly that minimizes the number of moving engine components required to rapidly move the inlet valve assembly to an open position when the piston arrives at a predetermined position within the cylinder. The contemplated inlet valve assembly cooperates with the crown portion of the piston to forcibly and rapidly move the inlet valve assembly to the open position.
Another improvement contemplates a mode switch valve actuator having a reduced number of engine components. The actuator includes a single cable coupled with each mode switch valve and a tension element for biasing the cable into a position corresponding to the engine start-up mode.